Embodiments of the present invention relate to an OP-amp circuit and, more particularly, to an OP-amp circuit configured to stably amplify voltage.
A nonvolatile memory device has the advantages of both a random access memory (RAM), enabling the writing and erasure of data, and a read only memory (ROM), retaining its data even without the supply of power, and so it has recently been widely used as the storage media of electronic devices, such as digital cameras, personal digital assistants (PDAs), and MP3 players.
The nonvolatile memory device includes a memory cell array, a row decoder, a page buffer unit, etc. The memory cell array includes a plurality of word lines extending in rows, a plurality of bit lines extending in columns, and a plurality of memory cell strings corresponding to the respective bit lines.
The memory cells have varying threshold voltages according to their program states. It is ideal that the threshold voltages of the memory cells have the same threshold voltage according to the state of data to be stored. However, when an actual program operation is performed on memory cells, the threshold voltages of the memory cells have a probability distribution in each area because of, for example, the characteristic of a memory cell and various external environments such as coupling influence.
The nonvolatile memory device includes single level cells (SLCs) capable of storing 1-bit of information and multi level cells (MLCs) capable of storing 2 or more bits of information.
A distribution of the threshold voltages of SLCs or MLCs exists within a range of approximately 4.5 V or less. An amplification circuit formed of a PMOS transistor is used as the output driver of a regulator for generating verification operation voltages. The breakdown voltage of the PMOS transistor is about 5 V.
As the number of bit data, such as 3 bits or 4 bits, which will be stored in a memory device, is increased, a threshold voltage distribution of memory cells gradually rises. When voltages for read or verification operations are generated using such a high threshold voltage distribution, a voltage amplification circuit formed of a known PMOS transistor device cannot be used.